1. Field of the Invention
The present invention relates to a film deposition apparatus.
2. Discussion of the Background
In a semiconductor device having a MOS (Metal Oxide Semiconductor) field-effect transistor structure, for example, an aluminum alloy of Al, Si and Cu is employed as a constituting material for a wiring layer. When a wiring layer containing aluminum is deposited on a silicon substrate constituting a semiconductor wafer (simply referred to as xe2x80x9cwaferxe2x80x9d hereinafter) by heat treatment, it is likely that aluminum of the wiring layer and silicon of the substrate will be inter-diffused to destroy a diffusion layer. The addition of silicon to the aluminum alloy thus prevents the above inter-diffusion from occurring. However, there occurs a problem that contact resistance is increased because silicon is precipitated out of the aluminum alloy onto the silicon substrate in a contact portion to form an n-type silicon layer and a p-type silicon layer, which causes a so-called pn junction, in accordance with miniaturization of the semiconductor device. A barrier metal layer is therefore interposed between the silicon substrate and the wiring layer in order to prevent silicon of the substrate and aluminum of the wiring layer from reacting on each other and prevent a pn junction from occurring.
A titanium alloy, such as TiN and Ti-W, or titanium, whose reactivity is lower than that of a conventionally-used tungsten alloy or tungsten and whose property is very stable toward heat or the like, has recently been adopted as a constituting material for the barrier metal layer.
Furthermore, instead of a sputtering system, a CVD (Chemical Vapor Deposition) system has recently been used as a film deposition apparatus for forming a barrier metal layer in order to improve a film coverage state in a step portion of a silicon substrate or a step coverage. For example, a thermal CVD system is used to form a barrier metal layer from TiN.
However, the dependence of deposition speed on temperature in processing (deposition) gas for depositing a TiN layer is higher than that in processing gas for depositing a conventional tungsten alloy film layer. If, therefore, the periphery of a wafer mounted on a mounting table is held by a clamp as in the thermal CVD system for depositing a tungsten alloy film, the clamp absorbs heat from the periphery of the wafer, and the distribution of temperatures of the substrate becomes nonuniform, with the result that a uniform barrier metal layer is difficult to form. In the thermal CVD system for depositing a TiN film, as shown in FIG. 6A, a wafer W is simply mounted on a mounting table 10, without using any clamp, to subject it to deposition processing.
However, in the thermal CVD system described above, the wafer W is simply mounted on the mounting table 10; therefore, as shown in FIG. 6A, a TiN-film layer 12 will be formed on the periphery of the wafer W as well as on the top thereof. After the barrier metal layer is deposited, generally, a metal film (wiring layer) 11 is formed on the barrier metal layer 12 and the metal film 11 is flattened. This flattening needs to be performed by CMP (Chemical Mechanical Polishing) since the metal film 11 has to improve in degree of flatteness in accordance with hyperfine structure and extremely-multilayer structure of a semiconductor device. If, however, the metal film 11 on the top of the wafer. W is flattened by CMP, the TiN-film layer 12 is not removed but remains on the periphery of the wafer W, as shown in FIG. 6B. In other words, there is a film which cannot be removed but remains on the periphery of the wafer W after the metal film 11 deposited on the barrier metal layer 12 is flattened. Consequently, the remaining peripheral film comes off in a processing chamber for post-processing and causes a contamination, thereby reducing yields.
If, moreover, the metal film 11 is flattened by, e.g., plasma etching, the TiN-film layer 12 is removed from the periphery of the wafer W simultaneously with the flattening. However, there is a limit to accurate control of plasma and thus it is difficult to increase a degree of flatness of the metal film.
The object of the present invention is to provide a film deposition apparatus capable of uniformly maintaining the distribution of temperatures of the entire surface of a target object to be processed, without exposing the periphery of the target object to processing gas.
The above object is attained by a deposition apparatus described below. A film deposition apparatus of the present invention includes a container forming a processing chamber for processing a target object; a mounting table which is provided in the processing chamber and on which the target object is mounted; a first heating apparatus provided in the mounting table, for heating the target object mounted on the mounting table; a first gas supply section provided in the container, for supplying processing gas into the processing chamber, the processing gas forming a high-melting-point metal-film layer on the target object mounted on the mounting table; a movable clamp for clamping a periphery of the target object and holding the target object on the mounting table; a second heating apparatus formed separately from the clamp, for heating the clamp indirectly; a gas flow path formed between the clamp and the second heating apparatus when the clamp is moved to a position where the clamp clamps the target object; and a second gas supply section for causing backside gas to flow into the gas flow path.
According to the above structure, when a target object is clamped, the clamp is brought into intimate contact with the periphery of the target object to block a space between the processing surface (top surface) of the object and the side thereof, and the backside gas prevents processing gas from flowing around the periphery of the object, so that it is difficult for the processing gas, which is supplied to the processing surface of the object, to reach the side of the object. Consequently, a high-melting-point metal-film layer becomes difficult to form on the periphery of the target object and thus the occurrence of particles due to exfoliation of the high-melting-point metal film can be minimized. Since, moreover, the clamp is heated by means of radiant heat from a heating source and backside gas, the temperature of the periphery of the target object is not lowered when the object is clamped and thus a uniform film can be deposited on the entire surface of the object.
If the gas flow path extends so as to pass the edge portion of the target object clamped by the clamp and the periphery of the mounting table, the processing gas does not reach the periphery of the target object, so that a high-melting-point film-layer can be prevented from being formed on the side of the object. Furthermore, in order to prevent the processing gas from flowing around the object, it is preferable to form the gas flow path such that the backside gas is exhausted in the direction of the outer circumference of the clamp.
In order to reliably prevent a high-melting-point metal-layer from being deposited to the side of the target object, it is preferable to adopt inert gas as the backside gas. Further, in order to minimize an influence of the backside gas emitted into the processing chamber upon the deposition processing, it is preferable to adopt the same gas as part of gas components constituting the processing gas, as the backside gas. When the gas flow path is shortened due to the restriction by the structure of the mounting table and tubing for supplying backside gas, and a predetermined conductance cannot be secured in the gas flow path, it is preferable to provide the gas flow path with a buffer section for controlling the conductance of the gas flow path.
If the clamp is shaped like a ring and clamps all of the edge portion of the target object against its inner side, entire peripheries of the object can reliably be clamped, and the periphery of the object can be maintained airtightly from the atmosphere of the processing chamber can be delimited airtightly. If, moreover, a tapered surface, which is brought into line contact with the object, is formed on the inner side of the clamp against which the object is clamped, the airtightness of the gas flow path is increased when the object is clamped against the tapered surface, and a high-melting-point metal-film can be prevented more reliably from being deposited to the periphery of the object. If the object is clamped against the tapered surface, given airtightness can be secured even when the object is placed inaccurately on the mounting table.
If the present invention is applied to the case where the uniform temperature distribution of the object to be processed is particularly required as in the case where a high-melting-point metal-film made of Ti or a Ti alloy is deposited, better results can be produced.